1. Field of the Invention
The present invention relates to tunable solid state lasers, and particularly to pulsed solid state lasers tunable over a wide spectral range with a narrow spectral line width in the output.
2. Description of Related Art
Tunable solid state lasers are being considered for a variety of applications, from remote sensing to medicine. See Peter F. Moulton, "Tunable Solid State Lasers Targeted for a Variety of Applications," LASER FOCUS/ELECTRO-OPTICS, August 1987, pp. 56-69. These applications for tunable lasers require a large tunable range, a long, useful life for the medium, and limited operator interaction during tuning.
Before tunable solid state lasers were targeted for applications requiring a broad spectral range, designers relied on dye lasers for such applications. However, dye lasers require use of liquid flowing dyes as the laser medium. Further, the tunable range of a specific dye is much smaller than the ranges of known tunable solid state media. Thus, when a tunable laser is required to cover a wide spectral range, the operator must change from dye to dye. Dye changing is a complicated procedure, making dye lasers inappropriate for many applications. In addition, dyes are typically toxic chemicals or solvents that are difficult to handle. Further, dyes used in tunable dye lasers usually have a short useful life and thus the dye needs to be changed even for applications having relatively narrow spectral requirements.
A prior art dye laser is disclosed in U.S. Pat. No. 4,255,718 entitled TRANSVERSELY PUMPED DYE LASER HAVING IMPROVED CONVERSION EFFICIENCY; invented by Richard L. Herbst.
Dye lasers are further typified by their application as laser amplifiers because of the very high gain of the dye medium. Accordingly, the internal energy of a dye laser is much lower than is typically encountered in solid state media that are lower gain and operate in the oscillation mode more readily. The control of line width in dye lasers has been demonstrated using gratings and beam expanders as disclosed in the Herbst reference cited above. However, because of the high gain of dye media, beam expansion on the order of 25 to 50 is required to achieve narrow linewidth operation, while simultaneously preventing damage to the gratings for dye laser applications. One would not expect, therefore, that a grating in combination with such a beam expander would be an operable means for assuring a narrow line width in the output of a solid state pulsed tunable laser used in an oscillator mode.
Using solid state media, it is desirable to have a narrow spectral line width. Prior art systems have been demonstrated that generate a 1 nanometer spectral width using injection seeding according to the Moulton article cited above. However, for many applications, it is desirable to have a much narrower spectral line width for a pulsed tunable solid state laser.